In x-ray spectrometry, compositional analysis of sample material is performed by identification of the characteristic x-rays emitted by each constituent atomic element during irradiation of the sample by electrons, x-rays, or ions. In 1913 J. Chadwick provided the first documented evidence that characteristic x-rays are generated by bombarding a sample with alpha particles emitted from a radioactive isotope. See J. Chadwick, Phil. Mag. 25, 193 (1913). When alpha particles strike the sample, atoms in the specimen are excited by the transfer of energy from the alpha particles and they emit characteristic x-rays or Auger electrons upon their de-excitation without high background x radiation that accompanies electron excited analysis. The x-rays are detected by an energy dispersive detector, their energy levels determined and subsequently analyzed. One system for alpha ray excited compositional analysis has been patented in U.S. Pat. No. 3,408,496 to Sellers, et al.
In addition to the characteristic x-rays, energetic electrons may be emitted from the sample under analysis and ionized particles may be produced from the residual atmosphere within the system or from the radioactive source itself. Impingement of any of these charged particles upon the detector produces an undersirable continuum of energy distributed throughout the x-ray spectrum in the form of background radiation which limits the sensitivity of the analysis. The thin beryllium window that usually protects solid state x-ray detectors absorbs most of the unwanted particles and thereby lowers the general level of background radiation. However, the beryllium windows also absorb the very low energy x-ray photons emitted by light atomic elements such as carbon, nitrogen, and oxygen. This invention eliminates the undersirable particle-induced background with magnetic or electrostatic fields and, hence, the need for the beryllium window absorber. Thus, a windowless detector has been used to detect, with very low background radiation, clearly resolved characteristic K-lines of the elements boron, carbon, nitrogen, oxygen, fluorine, sodium, and magnesium, as well as the L and M characteristic emission of other elements in the same energy region.